1. Field of the Invention
This invention pertains to the heat treatment of metal alloy castings and more specifically to the heat treatment of such castings in a fluidized bed used in conjunction with the making of the castings.
2. Description of the Prior Art
The basic operations of a foundry are molding, pouring, cooling, mold removal, sand reclamation, heat treating of the casting, and further heat treating and cooling for tempering purposes. In normal foundries, each operation is accomplished at a separate work station with considerable movement of material and equipment between each step.
Molding comprises the forming of sand or other granular material around a pattern to form two half-impressions of the part to be made. The box containing the sand impressions is then moved to a station where molten metal is poured into the cavity through a port in the sand. Generally, metal is melted in a furnace and then poured into a ladle which is then carried to the location where several molds are arranged for pouring.
The molds are then cooled and moved to a shake-out area where vibration or physical means is used to break and expel the sand from around the casting or castings. Each casting is then cleaned by blasting or other techniques and extraneous metal is removed.
The rough castings are then moved to a furnace where they are heated to a temperature of around 1600.degree. F. After a period of time, usually half an hour or so, a casting is removed and rapidly cooled with air, oil or water.
The casting is then heated again to a lower temperature, perhaps 1100.degree. F., and held for a time to temper and to provide satisfactory material properties.
The casting must then usually be blasted again to clean it and remove scale build-up during the high temperature operations.
Between each of the foregoing steps, there is considerable manpower necessary to move castings from one station to another. In a typical foundry where producing heat treated steel castings is accomplished by intermediate production runs, the amount of man hours necessary to produce castings is about 100 man hours per ton.
The process described herein, which can be characterized as a heat treating process in the environment of a foundry for making the castings, results in a savings of man hours required to produce the casting of about 80%. This is because ordinarily all operations are performed while the casting is still in the original sand mold.
Therefore, it is a feature of this invention to provide an improved heat treating environment for a metal alloy casting which is the sand bed, capable of being fluidized, used in the foundry production of the casting.
It is another feature of the present invention to provide an improved process of producing and heat treating a metal alloy casting, wherein the bed is alternately subjected to fluidizing and vacuumizing, the fluidizing advantageously providing a heat treating environment and the vacuumizing advantageously making the metallic molten flow more efficient while also cleansing the atmosphere of unwanted fumes and particle debris and supporting efficiently produced thin shell molds that can be used in such production.